As we all know, the random wind, gust, and the uncertainty caused the frequency and voltage of the electric power from the wind power unit, this electric energy is lack of use except for the electric installations
which have low-rise need for electric energy like heaters, we need to control and set the quality of the electric energy, the methods in common used are: constant speed constant frequency, variable speed constant frequency,
variable frequency control. The VSCF control method can not only control the quality of the electric energy, and also can capture the wind energy furthest, the active and reactive power can be independently adjusted by
decoupling control, and restrain harmonic, reduce the cost. The VSCF control projects we often use are: Asynchronous generator system, the exchange-fed generator excitation system, BDFM generator system,
permanent magnet generator system. Because the electronic equipment of the double-fed electrical generator play the pole only in the control loop, equipment capacity generally should not exceed 30% of the power output of
wind energy conversion system. The cost of equipment can be significantly reduced. Thus BDFM is a kind of wind energy conversion methods which have good prospect. BDFM, got rid of the slide loop and brush which
can be easily attrited, improved the reliability of wind energy conversion system.